July was a hot one. In fact, it was the second hottest in the history of Washington, DC meteorological records behind only last year. (This also makes it the second hottest month on record). As Justin reported yesterday, while we had far more 100-degree days this year, last year was hotter overall. Officially, 2011 was 0.5F hotter than 2012.
The three hottest Julys on record (dating back to 1871) have occurred in the last three years.
As Justin also noted, while July 2012 was hot, we did not see the same humidity levels that tortured us last July. The very dry Midwest was our source region at times, which kept our heat on the drier side, but also enabled the plethora of 100-degree readings (dry air heats up more readily than moist air).
Washington Reagan National saw five records broken in July: two record high minimums, two records highs, and one record low maximum. The hottest temperature ever recorded in the city was nearly tied July 7, but we fell short by one degree and possibly one minute (the thermometer hit 106F, but not for the required three minutes). For now, the 106 reading of July 1930 and August 1918 remain unmatched in the record books.
While we just missed the all-time record high, the average temperature (taking the high of 105 and low of 82 together) of 94 on July 7 was hottest on record for any day.
Here are some other notable stats:
* July 2012 set the record for most days at or above 95 with 16
* July 2012 set the record for most days at or above 100 with 7
* July 2012 tied (with 1930) the record for most consecutive days at or above 100 with 4
* July 2012 ranked 2nd for most days with lows at or above 80 with 4 (2011 had 7)
* One third of July days have record high low temperatures from the last three years (2010, 2011, and 2012)
Distribution of high temperatures
We spent most of the month in the 90s, but nearly tied for number of days with highs in the 80s and 100s. Our lone 71-degree high temperature on July 21st (that cloudy Saturday) was also a record low-maximum for the day. What an odd duck day in a hot month!
2012 temperatures year-to-date
Examining the track record of 2012 overall, the year is easily running as the warmest on record to date. With our warm winter, chart-busting March, and now hot summer, 2012 is the hottest year on record by a strong 1.7-degree margin currently. You can see the latest rankings listed to the right. Three other years (2011, 2010, 2002) from this relatively new century also made the cut in the January-to-July window.
From a precipitation perspective, Washington Reagan National continued its dry theme in July. However, due to the hit and miss nature of the convective rains, some areas in the metro region saw above normal precipitation.
An unofficial reading from my neighbor’s rain gauge in Columbia Heights reported a solid 8” total for the month compared to the 2.81” monthly value at National (Columbia Heights picked up .72” yesterday vs. only .03” at the airport!).
The tendency for dry conditions near the airport has contributed to 2012 ranking as the fifth driest year on record to date. Every month has seen below average precipitation.
Cause of the heat
The summer of 2012 follows two other very hot summers, and it is interesting to see how the three hot July patterns dominated. 2010 was more of a flat heat ridge across much of the nation. 2011 focused the hottest weather in the middle of the nation. And now 2012 did the same, but it was slightly to the west of 2011’s position. This slight shift probably contributed to our slightly cooler result.
What about August? A hotter-than-normal pattern looks to continue, but the strong, mid-continent “dome of drought” is starting to finally fade, especially around the edges. This means that we should see more variability to prevent as hot a result as July. We should see far less super-hot days, but probably should still average the month a few degrees hotter than normal. Keep in mind that normal temperatures in August is 1.7 degrees cooler than July! See the final nationally hot National Weather Service forecast for August.
For further information
The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly):
You can click on your closest airport location here:
See also Ian Livingston’s round-up of July climatology in Washington, D.C.
Jason Samenow and Ian Livingston contributed to this post